字符流中第一个不重复的字符

import java.util.*;
public class Solution {
    
    private int[] cache = new int[500];
    private List<Character> chs = new ArrayList<Character>();
    
    public Solution() {
        Arrays.fill(cache, 0);
    }
    
    //Insert one char from stringstream
    public void Insert(char ch) {
        chs.add(ch);
        cache[(int)ch] ++;
    }
  //return the first appearence once char in current stringstream
    public char FirstAppearingOnce() {
        for (int i=0; i<chs.size(); i++) {
            if (cache[(int)chs.get(i)] == 1) {
                return chs.get(i);
            }
        }
        return ‘#‘;
    }
}